1. Field of the Invention
The invention relates generally to aerodynamics. More specifically, the invention relates to the field of aircraft wing design.
2. Description of the Related Art
The accumulation of ice and other contaminants on aircraft wings has been an ongoing problem. With respect to ice buildup, artisans have taken a number of approaches to dealing with the problem. Some solutions have involved the administration of heat to the leading edge or other locations on the wing. Other techniques involve the use of chemicals to induce shedding. Additional solutions have involved the use of mechanical arrangements.
One mechanical arrangement involves the use of what is referred to as a “deice boot.” Deice boots include flexible sheets of rubber which are adhered to the leading edge of the wing and have span-wise inflatable tubes which are stitched into the rubber matting. When the tubes are inflated, the boot causes the accumulated ice to be pushed away from the leading edge surface. This allows the free stream of impinging air to strip the ice off of the wing and then carry it away. The boot is then deflated, but will be periodically reinflated to help minimize the amount of ice which collects on the wing. Thus, the cycled expansions mitigate the ice problem, but do not eliminate it completely.
One problem created by residual ice occurs at or near a stall. A stall is an aerodynamic condition in which the angle of an aircraft wing's chord line and the incoming air (the angle of attack) increases to a point that the lift begins to decrease. The angle at which this transition occurs is called the critical angle of attack. The critical angle depends on many wing design parameters, but normally represents the boundary between the wing's linear and nonlinear airflow regimes. Once the critical angle is reached, flow separation occurs. This flow separation dramatically decreases lift (sometimes suddenly), increases drag, and immediately shifts the aircraft's pressure center forward.
Depending on the aircraft's design, a stall can expose extremely adverse properties of balance and control—even in ideal conditions. But these issues are exacerbated when the aerodynamically ideal wing surfaces become contaminated with some foreign substance, such as ice or frost. Ice, frost, or other contaminating surface roughness can increase the speed at which the stall occurs. Thus, conventionally, ice buildup has been shown to interfere with control, especially as the speed and attack angle are near or at stall conditions.